Thermal Impacts on the Performance of Nanoscale-Gap Thermophotovoltaic Power Generators

The thermal impacts on the performance of nanoscale-gap thermophotovoltaic (nano-TPV) power generators are investigated using a coupled near-field thermal radiation, charge, and heat transport formulation. A nano-TPV device consisting of a tungsten radiator, maintained at 2000 K, and cells made of indium gallium antimonide (In_0.18Ga_0.82Sb) are considered; the thermal management system is modeled assuming a convective boundary with a fluid temperature fixed at 293 K. Results reveal that nano-TPV performance characteristics are closely related to the temperature of the cell. When the radiator and the junction are separated by a 20 nm vacuum gap, the power output and the conversion efficiency of the system are respectively 5.83 × 10⁵ Wm^-2 and 24.8% at 300 K, whereas these values drop to 8.09 × 10⁴ Wm^-2 and 3.2% at 500 K. In order to maintain the cell at room temperature, a heat transfer coefficient as high as 10⁵ Wm^-2 K^-1 is required for nanometer-size vacuum gaps. The reason for this is that thermal radiation since thermal radiation enhancement beyond the blackbody from a bulk radiator of tungsten is broadband in nature, while only a certain part of the spectrum is useful for maximizing nano-TPV performance. In future studies, near-field radiation spectral conditions leading to optimal performance characteristics of the device will be investigated.